How long should lice shampoo be left on the hair? - briefly
The shampoo designed for lice removal must stay on the scalp for about 10 minutes before rinsing, unless the label specifies a shorter interval of 5 minutes. Follow the manufacturer’s timing instructions precisely to ensure effectiveness.
How long should lice shampoo be left on the hair? - in detail
The contact time for a lice‑killing shampoo determines its effectiveness. Manufacturers typically recommend leaving the product on the scalp for a specific period, often expressed in minutes. The following points summarize the standard practice:
- Most over‑the‑counter formulations require a minimum of 10 minutes of exposure. This duration allows the active ingredient, such as permethrin or pyrethrin, to penetrate the exoskeleton of the lice and disrupt their nervous system.
- Some prescription products, especially those containing higher‑concentration dimethicone or malathion, advise a longer contact time—commonly 30 minutes. The extended period enhances the diffusion of the chemical into the egg (nits) membrane.
- Instructions may include a maximum limit, for example “do not exceed 30 minutes,” to prevent scalp irritation. Exceeding the recommended time does not increase efficacy and can increase the risk of adverse skin reactions.
- After the prescribed interval, the shampoo must be thoroughly rinsed with lukewarm water. Residual product should be removed to avoid irritation and to prevent re‑contamination from the shampoo itself.
- A second application is frequently advised 7–10 days later. This interval coincides with the hatching cycle of any surviving nits, ensuring that newly emerged lice are eliminated.
Additional considerations:
- Follow the label precisely; variations exist between brands. When the product label states «leave on for 15 minutes», that exact duration must be observed.
- For children under two years of age, many manufacturers restrict use or require a shorter exposure time, often 5 minutes, due to increased skin sensitivity.
- If the scalp shows signs of redness, itching, or burning during the exposure period, rinse immediately and consult a healthcare professional.
In summary, the recommended exposure time ranges from 10 minutes for most OTC shampoos to 30 minutes for stronger prescription formulas, with a follow‑up treatment scheduled a week later to address any newly hatched lice. Adhering strictly to the product’s timing instructions maximizes eradication while minimizing potential side effects.